Biogeography & relationships

Tom DiBenedetto tdib at OCEANCONSERVANCY.ORG
Wed Jul 10 12:23:00 CDT 2002

I will reply to two different posts by Robert in this one message.
 Robert Mesibov wrote:

> Tom DiBenedetto: If the
> character evidence
> indicated that a newly discovered New Zealand species were actually a
> hybrid of two
> Tasman species, would you advocate denying that conclusion simply because you
> could not immediately envision how the hybrid got to New Zealand?"
> No! The relationship story is unaffected, but the evolutionary picture is
> dramatically different.

Good. I think we actually agree. I seem to recall that the point of departure for this
thread was the question of whether spatial information was relevant to the enterprise
of reconstructing phylogenetic relationship - whether a conflict between a relationship
scheme and a biogeographic pattern should be resolved by allowing the
biogeographic information to affect the phylogenetic conclusion. I never intended to
imply that spatial information has no relevance to the broader question of how the
history of the taxa played out.

RM:This is very interesting, and it suggests that Tom & I are never going to
see eye to eye on certain issues. Tom is clearly saying that he is mainly
interested in the historical relationships between taxa.... However...I want to try to
understand how, when & where evolution has actually worked in particular groups.
...Relationship information isn't enough, I need other evidence,

It is not that I am only interested in the relationships, but I do think that the task of
discovering relationships is a coherent discipline unto itself and one which must be
persued with rigor and with a degree of independence from the process theories of
other evolutionary disciplines. A credible relationship scheme, arrived at through an
examination of all _relevant_ evidence is an enormously valuable tool to structure all
manner of evolutionary and comparative studies. I am led to belive that you may
agree with this when you say "I agree with Tom that unadorned relationships
are necessary and sufficient for a natural classification". The motivation behind my
remarks was simply to protect the integrity of systematics from the impulse to
synthesize prematurely - the interface between systematics and other evolutionary
studies (including biogeography) will only be fruitful if the integrity of each discipline is

RM: Another philosophical difference lurking here is how you view the
evolutionary narrative. If you think 'species' and relationships between
such objects, you're naturally led to focusing on the properties of
'species' and how to use those properties to understand the relationships
between 'species'. If like me you think 'lineages', you think more
architecturally about tree structure, i.e. the relationships between
objects with the objects removed.

I am not sure what you are getting at here. I always considered myself a "lineage"
type of guy, to the extent that my working conception of a species is merely a
terminal lineage branch. Given your subsequent comments regarding introgression
amongst populations, perhaps our difference is merely one of focus - coming from a
background in phylogenetic systematics, my concerns are with the relationships
amongst isolated lineage branches - relationships above the species level - where
niether taxa nor their relationship suffer from the "blurriness" you mention.

Tom diBenedetto

More information about the Taxacom mailing list